Problem: $ { \left[\begin{array}{rrr}{3} & {4} & {1} \\ {-1} & {-2} & {1}\end{array}\right]+\left[\begin{array}{rrr}{2} & {-1} & {-1} \\ {1} & {3} & {-2}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{3}+{2} & {4}+{-1} & {1}+{-1} \\ {-1}+{1} & {-2}+{3} & {1}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{5} & {3} & {0} \\ {0} & {1} & {-1}\end{array}\right]}$